What could cause excessive hair growth on my chin and back as a female under 30-years-old?

Could be PCOS ...: Polycystic ovarian syndrome (pcos) is the #1 cause of unwanted hair. To diagnose pcos, we need 2 out of 3 of: 1. Irregular/no periods 2. Clinical signs like acne, hair growth and/or blood tests showing too much male-type hormones 3. Ultrasound appearance of polycystic ovaries: high volumes or antral follicle counts. Adrenal gland problems can also cause xs hair. See an OB or rei / fertility md.